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  <div class="section" id="cmp0018">
<span id="policy:CMP0018"></span><h1>CMP0018<a class="headerlink" href="#cmp0018" title="Permalink to this headline">¶</a></h1>
<p>Ignore <code class="docutils literal notranslate"><span class="pre">CMAKE_SHARED_LIBRARY_&lt;Lang&gt;_FLAGS</span></code> variable.</p>
<p>CMake 2.8.8 and lower compiled sources in <code class="docutils literal notranslate"><span class="pre">SHARED</span></code> and <code class="docutils literal notranslate"><span class="pre">MODULE</span></code> libraries
using the value of the undocumented <code class="docutils literal notranslate"><span class="pre">CMAKE_SHARED_LIBRARY_&lt;Lang&gt;_FLAGS</span></code>
platform variable.  The variable contained platform-specific flags
needed to compile objects for shared libraries.  Typically it included
a flag such as <code class="docutils literal notranslate"><span class="pre">-fPIC</span></code> for position independent code but also included
other flags needed on certain platforms.  CMake 2.8.9 and higher
prefer instead to use the <span class="target" id="index-0-prop_tgt:POSITION_INDEPENDENT_CODE"></span><a class="reference internal" href="../prop_tgt/POSITION_INDEPENDENT_CODE.html#prop_tgt:POSITION_INDEPENDENT_CODE" title="POSITION_INDEPENDENT_CODE"><code class="xref cmake cmake-prop_tgt docutils literal notranslate"><span class="pre">POSITION_INDEPENDENT_CODE</span></code></a> target
property to determine what targets should be position independent, and new
undocumented platform variables to select flags while ignoring
<code class="docutils literal notranslate"><span class="pre">CMAKE_SHARED_LIBRARY_&lt;Lang&gt;_FLAGS</span></code> completely.</p>
<p>The default for either approach produces identical compilation flags,
but if a project modifies <code class="docutils literal notranslate"><span class="pre">CMAKE_SHARED_LIBRARY_&lt;Lang&gt;_FLAGS</span></code> from its
original value this policy determines which approach to use.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior for this policy is to ignore the
<span class="target" id="index-1-prop_tgt:POSITION_INDEPENDENT_CODE"></span><a class="reference internal" href="../prop_tgt/POSITION_INDEPENDENT_CODE.html#prop_tgt:POSITION_INDEPENDENT_CODE" title="POSITION_INDEPENDENT_CODE"><code class="xref cmake cmake-prop_tgt docutils literal notranslate"><span class="pre">POSITION_INDEPENDENT_CODE</span></code></a> property for all targets and use the
modified value of <code class="docutils literal notranslate"><span class="pre">CMAKE_SHARED_LIBRARY_&lt;Lang&gt;_FLAGS</span></code> for <code class="docutils literal notranslate"><span class="pre">SHARED</span></code> and
<code class="docutils literal notranslate"><span class="pre">MODULE</span></code> libraries.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">NEW</span></code> behavior for this policy is to ignore
<code class="docutils literal notranslate"><span class="pre">CMAKE_SHARED_LIBRARY_&lt;Lang&gt;_FLAGS</span></code> whether it is modified or not and
honor the <span class="target" id="index-2-prop_tgt:POSITION_INDEPENDENT_CODE"></span><a class="reference internal" href="../prop_tgt/POSITION_INDEPENDENT_CODE.html#prop_tgt:POSITION_INDEPENDENT_CODE" title="POSITION_INDEPENDENT_CODE"><code class="xref cmake cmake-prop_tgt docutils literal notranslate"><span class="pre">POSITION_INDEPENDENT_CODE</span></code></a> target property.</p>
<p>This policy was introduced in CMake version 2.8.9.  CMake version
3.16.5 warns when the policy is not set and uses <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior.  Use
the <span class="target" id="index-0-command:cmake_policy"></span><a class="reference internal" href="../command/cmake_policy.html#command:cmake_policy" title="cmake_policy"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">cmake_policy()</span></code></a> command to set it to <code class="docutils literal notranslate"><span class="pre">OLD</span></code> or <code class="docutils literal notranslate"><span class="pre">NEW</span></code>
explicitly.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior of a policy is
<span class="target" id="index-0-manual:cmake-policies(7)"></span><a class="reference internal" href="../manual/cmake-policies.7.html#manual:cmake-policies(7)" title="cmake-policies(7)"><code class="xref cmake cmake-manual docutils literal notranslate"><span class="pre">deprecated</span> <span class="pre">by</span> <span class="pre">definition</span></code></a>
and may be removed in a future version of CMake.</p>
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